This application relates to an electronic control system. It relates especially to a throttle/brake control system for a motorized wheel hub.
There are numerous vehicles in use today which have battery-powered electric motors to drive the wheels of the vehicle. These include bicycles, adult tricycles, wheelchairs, motor scooters, golf carts, all terrain vehicles, etc. In many such vehicles, the electric motor is mounted to the vehicle frame with the motor output being coupled to the wheels by way of a chain drive, gear train or the like. More preferably, the motor is incorporated right into the wheel hub thereby minimizing the size, weight, complexity and cost of the drive system. Examples of such in-hub motors are disclosed in U.S. Pat. Nos. 572,036; 2,514,460 and 3,921,741.
A particularly desirable, modular motorized wheel hub assembly for vehicles of this type is disclosed in U.S. Pat. No. 6,100,615, the contents of which is hereby incorporated herein by reference.
With modular motorized wheels of the type of interest here, it is essential that suitable control means be provided which are capable of applying the appropriate control voltages to the wheel motor to enable the wheel motor to operate in a reliable fashion. Invariably, such control means include a hand or foot-operated throttle or throttle/brake control which the vehicle operator may manipulate to accelerate the decelerate the associated vehicle. For the most part, conventional electric motor controllers, particularly those used to control electric bicycles, golf carts and other electric vehicles operate satisfactorily. However, they do have certain disadvantages which limit their wider use and application. More particularly, some such controllers are complex and costly. Others require a large number of moving, contacting parts or brushes which are prone to wear thereby limiting the useful life of the controller. Others are not suitable for all-weather outdoor applications, such as required on bicycles and other vehicles.
Also, those prior controllers used to control brushless motors of the type disclosed in the above patents often do not allow the motor to operate in a regenerative braking mode or if they do, they require the use of the Hall sensors or the like to sense the angular position of the motor rotor to effect communication of the motor in all four operating quadrants. That is, since, synchronous DC motors and other permanent magnet machines are frequently used in applications where direct control of the torque applied to the load is required, it is desirable to provide four quadrant operation, with both positive and negative torque and speed in such applications; see FIG. 10.
When the machine is operating in quadrants one and three in FIG. 10, it is operating as a motor and energy is being transferred from the DC source to the load. During operation in quadrants two and four the machine is used as a generator, and energy is transferred from the mechanical load to the DC voltage source. The motor shaft torque for a rotary machine (or force for a linear machine) is proportional to the winding currents applied to the motor and the torque constant of the motor, assuming that the motor is properly commutated. Proper commutation is required to generate a magnetic field in the motor stator windings that produce the desired force when acting against the permanent magnet field of the rotor. This is normally accomplished by utilizing a rotor position sensor or sensors to tell inverter circuitry driving the motor when to commutate the current from winding to winding to maintain this relationship.
The most common implementation of this principle is with a three phase brushless DC motor such as shown at M in FIG. 11, wherein the rotor position is detected with Hall effect devices H placed to indicate the angular position of the magnetic field produced by the rotor. In such a system, the commutation logic L switches the drive current to three high side switches S and three low side switches Sxe2x80x2 in an inverter I to maintain the proper field relationship. The rotating field of the rotor produces a back electromotive field (EMF) or voltage in the motor stator windings W. The applied voltage must overcome this back EMF for current to flow in the direction to produce motoring torque. The back EMF is proportional to the speed of the rotor and when the back EMF is equal to the applied voltage, motoring current cannot be generated. This speed is referred to as xe2x80x9cbase speedxe2x80x9d. Operation is normally limited to speeds below base speed. With operation below base speed, the back EMF produced is, by definition, less than the applied DC voltage. Operation of the machine as a generator, where mechanical energy is supplied to the DC source, requires that the back EMF voltage be boosted to a value at least equal to the applied voltage. This is normally accomplished by applying a voltage to the motor in the inverse polarity to the direction of rotation. This inverse commutation causes the stator current to increase rapidly. The increased current stores energy in the leakage inductance of the stator windings that, when the commutation is returned, adds to the back EMF to produce a voltage, thereby allowing current to flow in the stator. The FIG. 11 circuit produces this effect and generates a torque in the motor M that is independent of the direction of rotor rotation, and it works in all four quadrants shown in FIG. 10. The commutation logic for the six switches Sxe2x80x2, of that circuit is shown in FIG. 12. An example of such a brushless DC motor control is described, for example, in U.S. Pat. No. 6,034,493.
The motor M in FIG. 11 is thus driven in a six step per cycle sequence. This sequence is reversed to produce torque in the opposite direction. When the machine is operated in quadrants two and four (FIG. 10), the current produced by conduction of the switches S in the direction opposite to the rotation produces a current ramp up in the leakage inductance required to boost the back EMF to the source voltage level. The source current is measured by a current sensor C and the polarity of it is reversed by a switchable 1/xe2x88x921 amplifier A as a function of the direction of commutation. This arrangement maintains a unidirectional current in a hysteretic comparator H. The hysteresis in that comparator determines the frequency at which the commutation will be switched. The motor current is thus completely controlled, with the maximum and minimum being set by the hysteretic comparator H.
The circuit in FIG. 11 requires that the position of the rotor field be known to the commutation logic L. The rotating field of the rotor induces a voltage in the stator windings W that can be detected and used to determine the rotor position as well. However, such a position sensing system has a problem with operation at stall and low speeds where the back EMF voltage produced by the motor rotor is insufficient. There are several known methods of sensing the back EMF to produce the commutation logic. These methods require sensing the field in the stator winding W that is not being driven to determine the rotor position. However, when the commutation field is reversed for second and fourth quadrant operation, this logic does not produce the required results. Thus, conventional motor drive circuits based on such sensorless commutation methods do not allow operation in the second and fourth quadrant shown in FIG. 10. Rather, sensorless braking is normally accomplished by shorting out the stator windings and allowing the motor current produced to dissipate in the winding resistance. This can produce excessive currents which cannot be controlled as they do not flow through the current sensor C, but circulate within the stator windings W. Additionally, energy input from a mechanical source, such as a pedal crank in the case of a bicycle, is not recovered, but is dissipated in the motor, potentially producing excessive motor temperatures.
Alternate methods of producing braking torque have been explored and examples of these methods are given in U.S. Pat. Nos. 5,451,832 and 5,793,168. Both of these known control techniques provide a braking torque, but do not return the mechanical energy to the DC source. For simple traction applications, the direction of rotation does not reverse, but the torque still needs to be very well controlled in the first and fourth quadrants shown in FIG. 10.
What is desired, then, is a control system to produce second and fourth quadrant regenerative braking without the need for position sensing and that recovers the mechanical energy in an efficient manner. Additionally, the regenerative torque needs to be well controlled, as it is in the known Hall sensor-type position sensing circuit in FIG. 11.
Accordingly, it is an object of the present invention to provide an electronic control system that is particularly suitable for controlling a motorized wheel hub.
Another object is to provide a system of this type which is rugged and reliable and is capable of operating outdoors in extreme weather conditions for a prolonged period.
A further object of the invention is to provide a hand-operated control for a motorized vehicle which is relatively easy and inexpensive to make and to assemble.
Still another object of the invention is to provide such a control which is relatively immune to outside electrical influences.
Another object of the invention is to provide a control incorporating a rotary member and which produces positive and negative control signals proportional to the angular deviation of that member from a home position and which can be used to control a variety of electrical loads.
A further object of the invention is to provide a reliable, long lasting variable voltage throttle/brake control for a brushless DC motor or similar machine.
Another object of this invention is to provide a reliable control for a brushless motor that has a minimum of necessary wires connected to the motor.
A further object of the invention is to provide a control system which is sufficiently small, lightweight and compact to fit on a bicycle or other small vehicle.
An additional object is to provide a control circuit for interfacing a hand or foot-operated rotary control to a brushless DC motor which circuit provides suitable control voltages to enable the motor to operate at varying speeds in both forward and reverse torques as determined by the position of the rotary control.
A further object is to provide a control system for controlling a brushless DC motor which allows the machine to operate in a regenerative braking mode without the need for sensing the position of the motor""s rotor.
Yet another object of the invention is to provide such a control system that closely controls the regeneration torque developed by a DC machine.
Another object is to provide a system such as this which maintains full control of a brushless DC machine or AC synchronous machine when the machine is operating in both motoring and braking modes.
Yet another object is to provide such a system which controls the operation of a DC brushless motor at all speeds below base speed.
Still another object is to provide a hand-operated control system that can be mounted to standard bicycle without modifying the bicycle.
Other objects will, in part, be obvious and will, in part, appear hereinafter. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Briefly, our control system comprises a throttle/brake control comprising a plurality of contact tracks connected to a voltage source by way of a resistor ladder and a wiper which together produce positive and negative electrical signals. The tracks and the wiper are mounted for relative movement so that when the wiper is moved schematically from a home position toward one end of the resistor ladder (or vice versa), the control produces proportional positive electrical signals and when the wiper is moved toward the opposite end of the ladder from that home position (or vice versa), the control produces proportional negative electrical signals.
In a preferred embodiment of the invention particularly suitable for mounting to the handlebars of a bicycle, the resistor ladder and contact tracks are fixed to a first annular member encircling a handlebar grip segment and the wiper is fixed to a second annular member coaxial to the first member, the two members being rotatable relatively about their common axis in one direction or the other to produce the aforesaid proportional positive and negative electrical signals. Because the control is wholly resistive, it is rugged and reliable and immune to outside electrical influences, yet it is relatively easy and inexpensive to make in quantity.
As we shall see, the signals from the throttle/brake control are applied to a special sensorless control circuit to be described in detail later that produces drive signals for a motorized wheel hub mounted to a bicycle or other vehicle so as to selectively propel and brake the bicycle or vehicle at various rates depending upon the relative position of the two members of the throttle/brake control. Power for the control system is provided by rechargeable batteries which, along with the aforesaid control circuit, comprise a compact power unit which may be mounted to the frame of a bicycle or other vehicle without requiring any modification to that frame.